1. Technical Field
The following description relates to a display device, and more particularly, to a display device including an integrated touch panel.
2. Discussion of the Related Art
A touch panel is a kind of input device that is installed in an image display device, such as a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), an electroluminescence device (EL), an electrophoretic display (EPD), etc., to allow a user to input predetermined information by pressing (or touching) a touch sensor in the touch screen while viewing the image display device.
Recently, in order to implement a slim mobile terminal, such as a smart phone, a tablet PC, or the like, demands on an in-cell type display device including an integrated touch panel where elements configuring the touch panel are installed are increasing.
Hereinafter, an in-cell type display device including an integrated touch panel and a noise level according to application of a touch driving voltage will be described with reference to FIGS. 1, 2A, and 2B.
FIG. 1 is a view showing a display device including an integrated touch panel according to the related art. Specifically, FIG. 1 shows an in-cell self-capacitive type display device including an integrated touch panel.
In FIG. 1, an in-cell self-capacitive type display device including an integrated touch panel according to the related art includes a panel 10 where a plurality of electrodes 11 and a plurality of lines 12 connected to the plurality of electrodes 11, respectively, are formed, and a touch integrated circuit (IC) 20.
For example, the touch IC 20 may sense a change in capacitance due to a touch input applied to the plurality of electrodes 11 through a touch sensing unit 21.
FIGS. 2A and 2B are graphs showing a noise level according to application of a touch driving voltage in a display device including an integrated touch panel according to the related art.
In FIG. 2A, when touch driving voltages VDDT of about 0.7V and about 0.85V are applied to a plurality of electrodes of a first display device including an integrated touch panel, touch sensing results of changes in capacitance have noise levels of about 25 F and about 30 F, respectively.
In FIG. 2B, when touch driving voltages VDDT of about 0.7V and about 0.85V are applied to a plurality of electrodes of a second display device including an integrated touch panel, sensed signals of changes in capacitance have noise levels of about 60 F and about 30 F, respectively.
Here, a touch sensitivity is proportional to a signal to noise ratio (SNR), which is an average value of a sensed signal with a touch input and an average value of a sensed signal without a touch input divided by a maximum value of a noise without a touch input. Accordingly, as the noise increases, the signal to noise ratio decreases and the touch sensitivity is reduced.
The display device including an integrated touch panel has a deviation in noise level and the noise level of the display device including an integrated touch panel varies according to a driving circumstance. For example, the specific touch driving voltage may be an optimum value which minimizes the noise level in a display device including an integrated touch panel and may be a value which maximizes the noise level in another display device including an integrated touch panel. Thus, the noise level may vary across different display devices even when using the same touch driving voltage.